Caustic, e.g., sodium and/or potassium hydroxide, is the current commercial catalyst for the production of glycol ethers by the alkoxylation of an alcohol. These catalysts have been in use for over sixty years, and produce glycol ethers by way of a parallel-series reaction mechanism. The product mix from this process includes mono- and di-adducts (i.e., the lighter products) and tri-, tetra- and higher adducts (i.e., the heavier products). The market generally favors a product mix with a higher percentage of lighter products.
Moreover, in the production of glycol ethers from propylene oxide, both primary and secondary hydroxyl glycol ether product are made and because the former has toxicology issues associated with it, its presence in the final product mix is disfavored. The relative formation rate of the primary hydroxyl product increases with temperature which favors the use of low reaction temperatures, but caustic catalysts lose activity as the reaction temperature decreases. This, in turn, adversely affects the efficiency of the overall process.
Amines have been investigated as catalysts for the production of glycol ethers. These amine catalysts were primarily alkyl amines, e.g., triethyl amine, and these were found to be less active than caustic catalysts and produced larger amounts of impurities than the caustic catalyst system. In addition, these amine catalysts were found to quickly degrade by way of the Hofmann elimination reaction.
JP 2006/6045258 discloses the use of a tertiary amine having more than one active hydrogen as a catalyst in the manufacture of polyurethanes. JP 56-038323 discloses treating compounds having two or more active hydrogens with oxirane compositions in the presence of tetra-alkyl ammonium hydroxide to give polyalkylene glycol ether. Other patent disclosures of interest include GB 467228 (the production of glycol derivatives using a tertiary amine catalyst); FR 947250 (glycol derivatives using hexamethylenetetraamine); JP 1975/017976 (monoethoxylation of phenols using solvent and tertiary amines); JP 69-27570 (mono-glycol ethers of phenol produced by ethoxylation in the presence of a quaternary amine with a carboxylic acid); U.S. Pat. No. 3,560,574 (ethoxylation using trialkyl phosphines as catalysts); JP 1974/033183 (mono-glycol ethers of phenols prepared in the presence of trialkylbenzyl ammonium halides); and U.S. Pat. No. 3,910,878 (trialkylphosphonates and phosphines, phosphate esters as catalyst complexes with boron trifluoride).
References that discuss the use of heterocyclic amines as catalysts include Ionescu, M., et al, Imidazole, a High Efficiency Alkoxylation Catalyst, Polyurethanes Conference 2000, pp. 311-322 (use of imidazoles as a catalyst for the alkoxylation reaction for the production of polyether polyols for polyurethane manufacture); Ricciardi, F., et al., J. Mechanism of Imidazole Catalysis in the Curing of Epoxy Resin, Poly, Sci.—Poly. Chem., Vol. 21, 1475-1490 (1983) (imidazoles and amines used as catalysts for epoxy curing); Hreczuch, W., et al., Oxyethylation and Oxypropylation of Low Molecular Alcohols, Ind. Eng. Chem, Res., 1999, 38, 2225-2230 (effect of triethylamine catalyst on the oxyethylation and oxypropylation of methanol, ethanol and butanol); Poskrobko, H., et al., Oxyethylation and Oxypropylation of Low Relative Molecular Mass in the Presence of Amine-Type Catalysts, J. Chem. Tech. And Biotech., 2000, 75, 547-552 (the effect of an amine catalyst on the oxyalkylation of alcohols); WO 2003/042281 (the manufacture of polyether alcohols by alkoxylation of H-functional precursors with amines, e.g., imidazoles, as catalysts); US 2005/0004403 (the production of polyether alcohols using amine, e.g., imidazoles, catalysts); and JP 72-06744 (the production of glycol ether using a tertiary amine catalyst, including pyridine, picoline and quinoline).
Accordingly, the glycol ether industry has a continuing interest in identifying catalysts that not only favor the production of a product mix with more light products and less heavy products, but also that works well at a reduced reaction temperature.